1. Field of the Invention
This invention relates to a process for applying silicon-containing coating compositions and the use of light-fugitive dyes in priming compositions.
2. Description of the Prior Art
Protective coatings are ubiquitous in an industrial society. Building surfaces are coated to protect them from the effects of weather. Sensitive materials are coated to prevent corrosion. Lustrous materials are coated to maintain their brilliance. Materials needing further processing are coated to aid in subsequent handling or treatment.
While the utility of coating compositions is obvious, several problems are associated with their use. In many instances the location of a clear, colorless coating must be known with accuracy to insure complete coverage of a substrate or to identify "leave off" boundaries. Adding a colorant to the coating composition offers a solution to the aforementioned problems. Many coatings, however, must be clear after they are applied, rendering the use of a colorant impossible. On other occasions the prospect of an unsightly appearance of a surface brought about by accidental spillage or misapplication of the coating composition would discourage the use of a colorant in the coating composition. Furthermore, in certain applications a coating composition containing a colorant may undesirably transfer its color to "clean" areas during subsequent handling or processing operations.
The use of fugitive colorants is not new. The textile industry has long utilized fugitive dyes to temporarily identify a fabric or certain of its component parts and subsequently removed the dye by washing or leaching step. An interesting example of the use of a colorant as an indicator is taught by U.S. Pat. No. 3,509,081, to Gignac, wherein a reducible azo dye, is incorporated into a room temperature curing silicone composition. The azo dye undergoes a visible color change when exposed to the atmosphere, thereby indicating the extent of cure in the silicone composition. Of particular interest is French Pat. No. 1,467,175 which teaches the use of a light and/or air sensitive fugitive dye in a non-curing protective coating composition, wherein the fugitive dye must remain visible long enough to insure complete coverage of the article to be protected but must become invisible before the article is handled or further processed.
Currently, many silicon-containing coating compositions require the prior application of a primer to improve the adhesion of the coating composition to a surface. These priming compositions are either colorless or they contain a nonfugitive colorant and, consequently, present all of the problems of application and use that are described above for coating compositions in general. The addition of a fugitive colorant to colorless priming compositions as taught by this invention constitutes a new and useful improvement in the art.
As enumerated above, the prior art teaches the use of a water soluble or leachable colorant. Such a teaching, while being useful in the controlled environment of the textile mill, is of little value for the problems associated with the application of coating compositions to large areas outdoors, where no such environmental control exists. The prior art teaches the use of a silicone composition that contains a colorant which undergoes a useful color change, but not the desired loss of color, when exposed to the atmosphere. The prior art further teaches a coating composition that contains a fugitive dye that loses it color before the coated article is further processed. This teaching does not speak to the problem of priming compositions and their use.